The tumor microenvironment plays an important role in non-Hodgkin lymphoma (NHL) and the role intratumoral immune cells play in the pathology of lymphoma has been significantly understated. Intratumoral monocytes and macrophages are particularly important and our data demonstrate that intratumoral monocytes in NHL are highly immunosuppressive and support malignant cell growth. In preliminary work, we found that suppressive monocytic cells (SMCs) are abundant within the peripheral blood and tumor microenvironment in lymphoma patients and promote the survival of lymphoma cells. SMCs protect lymphoma cells from chemotherapy-induced cell death and promote lymphoma cell engraftment into severe combined immunodeficient (SCID) mice. Furthermore, we found that SMCs within lymph nodes express immunosuppressive ligands including B7-H1 (PD-L1, CD273), inhibit normal T-cell proliferation and promote the induction of FoxP3+ regulatory T cells. These preliminary studies suggest that SMCs have an effect on both malignant NHL cells and non-malignant intratumoral T-cells. Based on our results, we hypothesize that the intersection between the immune system and the malignant cell in NHL is the SMCs. In this proposal, we plan to understand whether monocytes are specifically recruited to sites of lymphoma and which specific chemokines could be inhibited to prevent SMC migration; how lymphoma cells induce SMCs to support their malignant cell growth and to suppress the host's antitumor immunity; and whether promoting monocyte/macrophage maturation or inhibiting their interaction with other cells, particularly in the presence of monoclonal antibodies, improves their anti-tumor function. Upon completion of this project, we expect to have a greater understanding of the role of monocytes and their progeny in NHL. Collectively our findings are likely to have a major impact by leading to an effective monocyte-directed therapeutic approach for patients with lymphoma.